Microdose therapy

ABSTRACT

Methods for treating vascular conditions associated with localized imbalance in vascular tone, which are hypothesized to be largely due to elevated endothelin (ET) are provided. The methods involve administration of nitric oxide (NO), agents which are able to provide NO, such as NO donors, agents which activate guanyl cyclase, such as YC-1, or agents which prolong the actions of endogenous NO or cyclic guanosine monophosphate (cGMP; a 2nd messenger molecule), such as phosphodiesterase (PDE) inhibitors. According to the invention, such agents are administered in minimal doses or microdoses by any route known in the art, so as to provide dosages which are about one half to about one twentieth (½ to {fraction (1/20)}) of those known to induce vasodilation in “normal” circulations. The low doses of these agents effectively alleviate vascular conditions associated with a reduction in NO production or an attenuation of NO effect, by restoring balance in vascular tone while exerting almost no systemic effect in normal vasculature.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/613,637, filed Jul. 11, 2000, now U.S. Pat. No. 6,423,683 which isDivisional Application of U.S. Application Ser. No. 09/469,649, filedDec. 22, 1999, now U.S. Pat. No. 6,165,975, which is a continuation ofPCT/CA98/00603, filed Jun. 22, 1998, and published as WO98/58633on Dec.30, 1998, which application claims the benefit of priority of U.S.Provisional Patent Application Nos. 60/050,491, filed Jun. 23, 1997, and60/086,750, filed May 27, 1998, the contents of all these applicationsare incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The field of invention is the treatment of conditions concerned withperipheral vasoconstriction. More particularly, the invention isconcerned with methods for establishing normal vascular tone in regionsof the circulation which demonstrate pathophysiology. In particular, theinvention concerns a method of treating erectile dysfunction byprovision of nitric oxide, nitric oxide producing agents, or activatorsof guanyl cyclase in small doses or microdoses, i.e., doses that do notinduce undesirable side effects, such as systemic vasodilation, undernormal conditions.

BACKGROUND OF THE INVENTION

It is widely known that administration of nitric oxide (NO), orcompounds which deliver NO (i.e., NO donors, NO producing agents) to asubject, can provoke powerful vasodilator responses. Such administrationis often accompanied by a number of undesirable side effects whichinclude headache, flushing, and hypotension.

The physiological role of NO has been described as that of a powerfulchronic vasodilator agent based on there being a marked increase invascular tone following NO synthase (NOS) blockade (Johnson et al., Am.J. Hypertens. 5:919, 1992; Tolins et al., Hypertens. 17:909, 1991). Therole of NO as a chronic vasodilator has only been inferred by indirectmeans, i.e., by removal of NOS activity. Endogenously, much moremultiplicity and overlap in the control of vasodilation can be inferredfrom the scientific literature. For example, vasodilation can be inducedby acetylcholine, bradykinin, adenosine, adenosine triphosphate (ATP),histamine, vasoactive intestinal polypeptide (VIP), and leukotrienes,amongst others. The actions of these endogenous modulators have beenshown to be dependent, at least in part, on the presence of theendothelium, an effect likely mediated by endothelial derived relaxingfactor/NO (EDRF/NO) (Garg, U. C. et al., J. Biol. Chem. 266:9, 1991;Garg, U. C. et al., J. Clin. Invest. 83:1774, 1989; Palmer, R. M. J. etal., Nature 327:524, 1987). Other vasodilator mechanisms exist which arenot endothelium dependent, such as β₂-adrenergic receptor activation,atrial natriuretic peptide (ANP) and certain prostaglandins. The actionsof NO have been suggested to be mostly cGMP-mediated via guanylatecyclase activation, although other mechanisms have been suggested. Forexample, Garg et al. (J. Biol. Chem. 266:9, 1991; J. Clin. Invest.83:1774, 1989) and others (Assender, J. W. et al., J. Cardiovasc.Pharmacol. 17(Suppl.3):S104, 1991; O'Conner, K. J. et al., J.Cardiovasc. Pharmacol. 17(Suppl.3):S100-S103, 1991) demonstrated adifference in the effects of NO-generating vasodilator agents ininhibiting vascular smooth muscle cell growth in culture; however, it isclear that NO can act not only as a vasodilator but also to inhibitvascular growth responses in a number of conditions (Farhy, R. D. etal., Circ. Res. 72:1202, 1993).

It has been believed and widely practised that NO, in humans andanimals, produced via sodium nitroprusside (SNP) infusion, causesvasodilation in peripheral vasculature at doses greater than 10 μg/kgper min. It has recently been determined that NO also performs afunction through interaction with endothelin (ET) (Banting et al., J.Hypertens. 14:975, 1996; Richard et al., Circulation 91:771, 1995).Prior to this time, ET had been believed to play a minimal role inmaintaining tone in the peripheral microvasculature and to have littleimpact on the state of contraction of smooth muscle in those vessels.Recent studies have indicated (Banting et al., J. Hypertens. 14:975,1996) that ET is under the inhibitory control of NO and thatadministration of NOS inhibitors results in elevated levels of ET.

Endothelins were first described in 1988 and have been shown to bepowerful vasoconstrictors, predominantly found in vascular endotheliumand, since that time, numerous ET antagonists and their pharmaceuticallyacceptable salts have been identified and can be obtained commercially(e.g., Sigma, American Peptides). Detailed descriptions of the chemicalstructures of various ET antagonists may be found in U.S. Pat. No.5,284,828 issued Feb. 8, 1994 to Hemmi et al., U.S. Pat. No. 5,378,715issued Jan. 3, 1995 to Stein et al., and U.S. Pat. No. 5,382,569 issuedJan. 17, 1995 to Cody et al. In addition, U.S. Pat. No. 5,338,726 issuedAug. 16, 1994 to Shinosaki et al. describes the chemical structure of ETconverting enzyme inhibitors. To date, however, antagonists of ET havenot been approved for therapeutic use, although a number ofinvestigators have postulated that ET antagonists could be used forconditions ranging from renal failure, endotoxic shock, asthma, angina,or diabetes to pulmonary hypertension and possibly other indications.

Under normal physiological conditions, ET can be found in almost allparts of circulation at very low levels. In general, in the normalrodent circulation ET is not found in elevated quantities and appears tohave little detectable role in the normal regulation of vascular tone,i.e., there is no appreciable decrease in blood pressure when an ETantagonist is administered by injection in normal circulation. Further,at present there does not appear to be any evidence suggesting that ETplays a physiological role even in a small portion of the circulationunder normal circulatory conditions in experimental models. However, itis likely that the systemic circulation may appear to be normal when, infact, specific regions of the circulation are undergoingpathophysiological changes such as occurs in conditions such as erectiledysfunction (ED) (Adams et al., Int. J. Impot. Res. 9:85-91, 1997).

Consequently, there are cardiovascular conditions which aretraditionally treated in human beings by significant doses of NO or NOdonors, such as glyceryl trinitrate (GTN) (0.2 mg/h and greater).However, these doses are known to induce systemic vasodilation andprovoke considerable overall systemic side effects (The, L. S. et al.,Brit. J. Rheum. 34:636, 1995). This is particularly so where apathological condition exists only in certain major organs (e.g., heart,kidney, liver). As a result, a satisfactory method for promotingrecovery of normal perfusion pressure in organs with certain pathologieswithout producing overall systemic hypotension has not been discovered.

Based on the understanding that a significant portion of underlyingproblems in clinical erectile dysfunction relates to “vascular”mechanisms, much of the current state-of-the-art research involvesdetermining the contribution that the different vascular effectorcontrol systems make in normal and pathophysiological states. There issubstantial understanding of hemodynamic events that lead to anerection, and yet the quantitative roles of each of the neuroeffector,humoral and local systems in these events remain poorly described. Since1990, NO has been considered the primary non-adrenergic non-cholinergicneurotransmitter in the penis and has been presumed to be the primarymediator of corporal relaxation during erection (Ignarro L. J. et al.,Biochem. Biophys. Res. Comm., 170:843, 1990).

It is well established that, for an erection to occur, neurally mediated(autonomic) vasodilation of the penile arterial blood vessel and thetrabecular meshwork takes place (Lue, T. F. et al., J. Urol. 137(5):829,1987) permitting increased blood flow into the cavernous bodies of thepenis. The expanding intra corporal volume compresses the effluent veinsthat lie between the erectile tissue and the surrounding fibrous,relatively inelastic, tunica albuginea. The outflow capacity is therebydecreased and entrapment of blood ensues, resulting in thetransformation of the flaccid penis into its erect state (Lue, T. F. etal, J. Urol. 137(5):829, 1987; Juenemann, K. P. et al., J. Urol.136(1):158, 1986; Lue, T. F. et al., J. Urol. 130:1237, 1983; Weiss, H.et al., Ann Intern. Med. 76:793, 1980). The level of arterial vasculartone (i.e., blood pressure) is one of critical importance in thisprocess, although adequate perfusion pressure is also a necessaryfactor. The converse, detumescence, is mediated by the sympatheticnervous system (Saenz de Tajada, I. et al., Am. J. Physiol. 254:H459,1988; Juenemann, K. P. et al., Br.J. Urol. 64, 1989).

The issue of “impotence” (defined as “a pattern of persistent orrecurrent inability to develop or maintain an erection of sufficientrigidity for successful coitus”) was discussed at a consensus conferenceof the National Institutes of Health (NIH) in Washington in December1992 and has been clearly identified as having a wide range of causativeor associated factors. The Massachusetts Male Aging Study (MMAS) hasprovided an updated view of the epidemiology of erectile dysfunction. Itis accepted that the prevalence of impotence increases with age (KinseyA. C. et al., “Sexual Behaviour in the Human Male”, W. B. Saunders:Philadelphia, 1948). Severe or complete ED increases from 5 to 15%between 40 and 70 years of age, (Feldman, H. A. et al., J. Urol. 151:54,1994). ED has been shown to be “directly correlated with heart disease,hypertension, diabetes, associated medications, indices of anger anddepression, and inversely with serum dehydroepiandrosterone, highdensity lipoprotein, cholesterol and an index of dominant personality.”

It is now estimated that in North America there are more than 30,000,000men with some form of ED, a significant increase from the figure of10,000,000 quoted just 10 years ago (Shabsigh, R. et al., Urology 32:83,1988; Whitehead E., Geriatrics 43(2):114, 1988; Furlow, W. L. et al.,Med. Aspects Human Sexuality 19:13, 1985). From these figures it is alsoreasonable to estimate that as many as three million Canadian men mayhave a degree of ED. The direct cost of treating impotence issignificant. Reliable figures from 1985 show that the cost of treatingimpotence exceeded 146 million dollars in the United States in that yearalone (National Center for Health Statistics) and this number is justthe estimated market size for one type of injectable therapy. Thesecondary effects and indirect costs associated with ED suggest thatimpotence and sexual dysfunction are medical icebergs. The consequencesof sexual dysfunction may be seen in strains on the host relationshippotentially leading to marital breakdown, violence, work relatedsequelae, deviant sexual behaviour and impacts on children, whenpresent, that can carry the damage into a new generation of unwantedbehaviours. If ED underlies even a small but significant percentage ofmarital and family breakdown, then it adds vastly to the social andeconomic burden in society. The pragmatic issue is that large numbers ofmen are now being treated for ED and most of the treatments are fairlyblunt instruments (e.g., intracavernosal injection (ICI)) of mixedvasoactive compounds, penile prosthesis insertion) with significant costand complications (ICI: pain, priapism, dislike of the technique;prostheses: reoperation, infection, distortion of body image).

Administration of NO, or compounds which are able to deliver NO, havebeen suggested as possible therapies; however, these agents can provokepowerful yet inappropriate vasodilator responses (Brock et al., J. Urol.150:864, 1993). Such administration is often accompanied by a number ofundesirable side effects related to systemic vasodilation which includeheadache, flushing, and hypotension. Consequently, there is a real needto provide methods whereby ED and other vascular disease may be quicklyand effectively treated without any inappropriate side effects.

SUMMARY OF THE INVENTION

Problems associated with localized imbalance in vascular tone, such asseen in ED, and which are hypothesized to be largely due to elevated ET,may be relieved by the administration of agents which are able toprovide NO, by direct administration of NO, or by administration of anagent or agents which activates guanyl cyclase, such as, for example,YC-1, or other agents which prolong the actions of endogenous NO or ofcGMP (a 2nd messenger molecule), such as phosphodiesterase (PDE)inhibitors, in minimal doses or microdoses, which heretofore had notbeen thought to result in effective treatment of an imbalance invascular tone.

In the normal physiological state, there are sufficient quantities of NOpresent in the vasculature to maintain appropriate levels of ET (Bantinget al., J. Hypertens. 14:975, 1996). The addition of further NO haslittle impact on the effect of ET and consequently any furthervasodilation seen in such normal smooth muscle in the vasculature islikely attributable to NO's effects on the generation of cGMP, with cGMPresulting in decreased levels of Ca⁺⁺. In certain pathologicalconditions, such as diabetes and cardiovascular disease, and/or as aconsequence of age, tissue is unable to provide satisfactory levels ofNO in order to suppress normal levels of ET present in smooth muscletissues.

As such, physiological conditions where NO production is reduced in aspecific local circulation, such as male ED, indicate that suppressionof ET activity should offer an effective treatment. Consequently, inaccordance with this, the present invention provides for the use of anagent or agents which directly or indirectly generates NO at dosageswhich are about one half to about one twentieth (½ to {fraction (1/20)})of those known to induce vasodilation in “normal” circulations, andconsequently exert almost no effect in the normal vasculature. As suchthese low doses, or “microdoses” are hypothesized to normalize thebalance between NO and ET. The range of about ½ to about {fraction(1/20)} is derived from the observation that at doses which are belowabout ½ the normal dose, systemic effects are generally no longer seen.At about {fraction (1/20)} the normal dose, however, the desired effectis also generally no longer observed, i.e., there is no effect.

According to one aspect of the present invention the concept of“low-dose” agents which directly or indirectly generate NO, or prolongthe action of NO, or enhance the cGMP 2nd messenger system, such as PDEinhibitors, is also applicable to any other peripheral pathologicalconditions where, regardless of the origin, NO is at least partiallyinhibited.

According to a further aspect of the present invention, there isprovided a method for restoring normal vascular tone in vasculaturewhere NO levels are depleted and restoration of such levels may beachieved by addition of NO at levels which do not appreciably alternormal systemic vascular tone.

According to yet a further aspect of the present invention there isprovided a method to treat any condition where NO levels are at leastpartially inhibited or reduced, wherein the method comprisesadministration of NO or one or more NO donors, or one or more agentswhich activate guanyl cyclase, by oral, sublingual, buccal, intravenous,transdermal, or any other effective route, in concentrations that areabout ½ to about {fraction (1/20)} of a concentration required to inducevasodilation in “healthy” or normal regions such as the coronary orskeletal muscle vasculature. Preferably, the concentrations of themethod of the present invention are about one quarter to about onetwentieth (¼ to {fraction (1/20)}) of a concentration required to inducevasodilation in “healthy” or normal regions such as the coronary orskeletal muscle vasculature. Still more preferably, the concentrationsof the method of the present invention are about one eighth to about onesixteenth (⅛ to {fraction (1/16)}) of a concentration required to inducevasodilation in “healthy” or normal regions such as the coronary orskeletal muscle vasculature.

According to one aspect of the present invention there is provided amethod to treat instances of renal disease associated with excessivevasoconstriction where NO levels are at least partially inhibited,wherein the method comprises administration of NO or one or more NOdonors, or one or more agents which activate guanyl cyclase, by oral,sublingual, buccal, intravenous, transdermal, or any other effectiveroute, in concentrations that are about ½ to about {fraction (1/20)} ofa concentration required to induce vasodilation in “healthy” or normalregions of the circulation such as the coronary or skeletal musclevasculature.

According to a another aspect of the present invention there is provideda method to treat premature aging of the skin associated withinappropriate vasoconstriction of the skin vasculature which isassociated with at least partial inhibition of NO levels in the skin,wherein the method comprises administration of NO or one or more NOdonors, or one or more agents which activate guanyl cyclase, by oral,sublingual, buccal, intravenous, transdermal, or any other effectiveroute, in concentrations that are about ½ to about {fraction (1/20)} ofa concentration required to induce vasodilation in “healthy” or normalregions such as the coronary or skeletal muscle vasculature.

According to a further aspect of the present invention there is provideda method to treat male ED caused at least by partial inhibition of NO inthe penile vasculature wherein the method comprises administration of NOor one or more No donors, or one or more agents which activate guanylcyclase, by oral, sublingual, buccal, intravenous, transdermal, or anyother effective route, in concentrations that are about ½ to about{fraction (1/20)} of a concentration required to induce vasodilation in“healthy” or normal regions such as the coronary or skeletal musclevasculature.

According to yet a further aspect of the present invention there isprovided a method to treat ED comprising administering to a subject inneed thereof a quantity of glyceryl trinitrate (GTN) by any route, forexample, oral, sublingual, transdermal, intravenous, or inhalation, thatprovides plasma concentrations of below about 250 pg/ml of the GTN, sothat ED is treated.

According to one aspect of the present invention there is provided alow-dose transdermal “patch” with short term release of, for example,GTN or any other effective provider of NO, such as, for example, one ormore NO donors or one or more agents which activate guanyl cyclase, overa period of time less than 6 hours (as opposed to 12, 18 or 24 hourrelease), which restores normal vascular tone in an affected localvascular bed, such as the pudendal or penile vasculature of men with ED,without inappropriately affecting systemic vascular tone or causinghypotension, and preferably, but not necessarily, without inducingtolerance (Bennett et al., Circ. Res. 63:693, 1988) to the effectsand/or biotransformation of a NO releasing compound to its releasingform.

According to a further aspect of the present invention, there isprovided a low dose or microdose “patch” with long term release of, forexample, GTN, or any other effective provider of NO, such as, forexample, one or more NO donors, or one or more agents which activateguanyl cyclase, over a period of time greater than 6 hours (typically 12to 24 hour release), which restores normal vascular tone in an affectedlocal vascular bed, such as the pudendal or penile vasculature of menwith ED, without inappropriately affecting systemic vascular tone, andpreferably, but not necessarily, without inducing tolerance to theeffects of a NO releasing compound and/or biotransformation of a NOreleasing compound to its releasing form.

According to a further aspect of the present invention there is provideda method to treat female sexual dysfunction (SD) wherein the methodcomprises administration of NO or one or more NO donors, or one or moreagents which activate guanyl cyclase, by oral, sublingual, buccal,intravenous, transdermal, or any other effective route, inconcentrations that are about ½ to about {fraction (1/20)} of aconcentration required to induce vasodilation in “healthy” or normalregions such as the coronary or skeletal muscle vasculature.

According to yet a further aspect of the present invention there isprovided a method to treat SD comprising administering to a subject inneed thereof a quantity of GTN by any route, for example, oral,sublingual, transdermal, intravenous, or inhalation, that providesplasma concentrations of below about 250 pg/ml of the GTN, so that SD istreated.

According to one aspect of the present invention there is provided alow-dose transdermal “patch” with short term release of, for example,GTN, or any other effective provider of NO such as, for example, one ormore NO donors or one or more agents which activate guanyl cyclase, overa period of time less than 6 hours (as opposed to 12, 18 or 24 hourrelease), which restores normal vascular tone in an affected localvascular bed, such as the pudendal, cervical or vaginal vasculature ofwomen with SD, without inappropriately affecting systemic vascular toneor causing hypotension, and preferably, but not necessarily, withoutinducing tolerance (Bennett et al., Circ. Res. 63:693, 1988) to theeffects and/or biotransformation of a NO releasing compound to itsreleasing form.

According to a further aspect of the present invention there is provideda low dose or microdose “patch” with long term release of, for example,GTN, or any other effective provider of NO, such as, for example, one ormore NO donors or one or more agents which activate guanyl cyclase, overa period of time greater than 6 hours (typically 12 to 30 hour release),which restores normal vascular tone in an affected local vascular bedsuch as the pudendal, cervical or vaginal vasculature of women with SDwithout inappropriately affecting systemic vascular tone, nor inducingtolerance to the effects of a NO releasing compound and/orbiotransformation of a NO releasing compound to its releasing form.

Definitions GTN glyceryl trinitrate ISMN isosorbide 5-mononitrate ISDNisosorbide dinitrate PETN pentaerythritol tetranitrate ETN erythrityltetranitrate SNP sodium nitroprusside SIN-1 3-morpholinosydnoniminemolsidomine SNAP S-nitroso-N-acetylpenicillamine SNOGS-nitrosoglutathione NOHA N-hydroxy-L-arginine cAMP cyclic adenosinemonophosphate cGMP cyclic guanosine monophosphate L-NAME N^(ω)nitro-L-arginine methyl ester IP₃ inositol-1,4,5-triphosphate RIHP renalinterstitial hydrostatic pressure T tumescence R rigidity

“Applying various forms of NO” as used herein includes administering NOdonor or NO producing agents.

“Enhancing penile erection” as used herein is understood to meanincreasing physical size and improving tumescence and/or rigidity of apenis, preferably so that it is capable of intromission.

“Erection of good quality” and “effective erection” are used hereininterchangeably to mean adequate for vaginal penetration (i.e.,intromission, or intercourse).

“NO donor”, “NO producing agent”, “NO delivering compound”, “NOgenerating agent” and “NO provider” are used interchangeably in thisspecification and include all compounds which donate NO throughbiotransformation, compounds which generate NO spontaneously, compoundswhich spontaneously release NO, or any other compounds which otherwisegenerate NO or an NO-like moiety and include: glyceryl trinitrate,isosorbide 5-mononitrate, isosorbide dinitrate, pentaerythritoltetranitrate, erythrityl tetranitrate, sodium nitroprusside,3-morpholinosydnonimine molsidomine, S-nitroso-N-acetylpenicillamine,S-nitrosoglutathione, N-hydroxy-L-arginine, S,S-dinitrosodithiol, or NOgas, or a functional equivalents thereof. In some cases, NO is generatedby activation of guanyl cyclase.

“Penis” as used herein may be interpreted to apply equally to clitorisin so far as there is substantial equivalence between penile andclitoral erectile tissue. “Sexual dysfunction” (SD) as used hereinincludes aspects of female dysfunction and urogenital aging such asdecreased vaginal lubrication, decreased vaginal engorgement, painduring intercourse such as, for example, dyspareunia, urogenitalinfections; and urogenitalia as affected by post-menopause, diabetes,vascular disease, estrogen depletion conditions, sexual dysfunction, andidiosyncratic vaginal dryness, respectively.

“Various forms of NO” as used herein is understood to mean any one ofNO^(·), NO⁺ and NO⁻, preferably NO⁺ and NO⁻, and can include as analternative CO (carbon monoxide) in its various forms, which produces anequivalent effect to NO.

“Without inappropriately affecting systemic vascular tone” as usedherein means not affecting mean arterial pressure so as to produceinappropriate systemic vasodilation with effects such as hypotension,headache, flushing.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, wherein:

FIG. 1 is a graphical representation of results from measurements ofmean arterial blood pressure in rats and illustrates the differentialimpact on mean arterial pressure (mmHg) of infusions of sodiumnitroprusside in control and L-NAME treated rats.

FIG. 2 is a representative tracing of measured mean arterial pressure ina rat demonstrating the contrasting effect of low level infusions ofsodium nitroprusside in control and acute L-NAME treated rats.

FIG. 3 is a graphical representation of measurements of mean arterialblood pressure illustrating an enhanced glyceryl trinitrate doseresponse curve in rats treated with control and L-NAME, acutely.

FIG. 4 is a schematic diagram depicting a range representative of a“normal” vascular controlling “window” of NO with comparisons of controland L-NAME treated rats.

FIG. 5 is a representative tracing of changes in mean arterial pressureand renal interstitial hydrostatic pressure (RIHP) in respect of renalcirculatory blockade of NO synthase.

FIG. 6 is a representative tracing of changes in mean arterial pressureand renal interstitial hydrostatic pressure (RIHP) in respect of thecapacity of L-arginine to induce decreases in RIHP in connection withthe renal circulation.

FIG. 7 is a representative tracing of changes in mean arterial pressureand renal interstitial hydrostatic pressure (RIHP) in respect ofdecreasing RIHP following removal of L-arginine in the renalcirculation.

FIG. 8 is a graph comparing the sensitivity of mean arterial pressure tothe NO donor sodium nitroprusside (SNP, right) and toisopropylnorepinephrine (INE, left), in the presence and absence of theNO synthase blocker L-NAME.

FIG. 9 is a cumulative dose response curve of mean arterial pressure toprazosin, an α₁ blocker, in the presence and absence of NO synthaseblockade (L-NAME).

FIG. 10 is a graph illustrating a change in mean arterial pressure fromcontrol conditions in the presence of SNP low-dose, SNP+L-NAME, andL-NAME alone.

FIGS. 11 and 12 are graphs illustrating a dose-response relationship ofmean arterial pressure for different doses of the nitric oxide donorsSNP (top panel) and GTN (bottom panel), before and after both nitricoxide synthase blockade (L-NAME) and endothelin receptor antagonism(PD145065).

DETAILED DESCRIPTION OF THE INVENTION

The physiological role of NO has been described as that of a chronicvasodilator agent acting to persistently “offset” the actions of anumber of vasoconstriction systems. However, as discussed by Banting etal. (J. Hypertens. 14:975, 1996), based on this rationale, this wouldreveal that the NO vasodilator system would normally have an overallactivity level at close to 70% of the NO system's maximal capacity,leaving the system little reserve or gain to protect against furtherdeviations in mean arterial pressure and blood flow homeostasis.

Banting et al. (J. Hypertens. 14:975, 1996) proposed that the chronicrole of NO, in vivo, is not that of a chronic vasodilator system butrather an inhibitor of the activity of local vasoconstrictor agents,such as ET. That is, the hypertension following blockade of NOproduction was completely reversed with the administration of an ETreceptor antagonist. This finding, combined with the understanding thatET appears to play almost no role in the “normal” physiological controlof resting mean arterial pressure, indicates that the function of NO maybe different than previously proposed. The results of the QuantitativeStudy as detailed below, in summary, indicate that:

(i) the amount of NO required to completely restore mean arterialpressure in L-NAME treated rats from hypertensive levels is much lessthan that required to lower mean arterial pressure under controlconditions;

(ii) the increase in sensitivity to NO and NO donors allows for aslittle as {fraction (1/20)}th of the standard concentration to provide agiven vasodilator response in NO synthase blockade rats;

(iii) the level of NO required to completely reverse the hypertension inthe chronic phase of L-NAME induced hypertension without altering bloodpressure in control rats is at the same level as required to reverse thehypertension following acute NO synthase blockade; and

(iv) the similar mean arterial pressure lowering, in both treated andcontrol rats, that occurred with the administration of “high”concentrations of sodium nitroprusside suggests that signallingprocesses have been “normalized” at approximately 10-12 ug/kg per minuteof sodium nitroprusside infusion.

Banting et al. (J. Hypertens. 14:975, 1996) have suggested that a majorrole of NO is not to function as a chronic vasodilator, but rather achronic inhibitory regulator of ET-mediated vasoconstriction. In thatstudy it was demonstrated that ET-mediated vasoconstriction does notcontribute to the maintenance of vascular tone in a circulation with anintact NO generating system. Also, it was demonstrated that almost theentire L-NAME induced hypertension was both prevented and/or reversedvia the administration of an ET receptor antagonist. The resultsdetailed below under the heading Quantitative Study quantitate theexogenous level of NO required to restore this regulatory balance and,taken together, we propose that NO functions to suppress ET-mediatedvasoconstriction within a physiological “window” as illustrated in FIG.4, in a manner which is unrelated to its direct role as a vasodilatorsubstance. Indeed, it is proposed that the mechanism of action of the NOdonors delivered at the micro doses disclosed herein, are notvasodilatory; rather they act to suppress the endogenous role ofendothelin.

These conclusions and their applicability to other microcirculations aresupported by studies conducted in the kidney in connection withmeasurements of renal interstitial hydrostatic pressure and meanarterial pressure as reported below under the heading: Effect of NO inRenal Vasculature.

In a further application of the present invention, studies conducted inhuman males with a low-dose “patch” with up to 3 hours of release ofeffective NO, demonstrate that providing a “microdose” of NO restorednormal erectile function. The results of these studies are detailedbelow under the heading: Clinical Data: For erectile dysfunctionreversal with microdoses of NO.

Accordingly, the present invention provides a method for restoringnormal vascular tone through the use of an agent or agents whichdirectly or indirectly generate(s) NO at dosages of about ½ to about{fraction (1/20)} of those currently used in clinical applications.

The method of the present invention is also applicable to any otherperipheral pathological conditions where regardless of the origin, NO isat least partially inhibited. In respect of the conditions detailedbelow evidence in the literature demonstrates that the production of NOis, at least partially, inhibited. This leads to an imbalance between NOand ET in favour of ET. The method of the present invention restoresthis balance with ‘quantities’ of NO that do not induce vasodilation, ornot appreciably, in ‘healthy’ or non-NO deficient circulations.Conditions wherein the present invention has application include anycondition where regional circulation exhibits inappropriatevasoconstriction, such as, for example, ED, conditions associated withfemale sexual dysfunction involving vaginal and/or pelvic circulation,Raynaud's phenomenon (a condition of the fingers with constrained bloodflow), as well as conditions associated with inappropriatevasoconstriction in, for example, cutaneous and/or dermal (for examplein reconstructive surgery, as well as scleroderma and diffuse cutaneoussystemic sclerosis), cerebral, and renal circulations. Concerning ED,the therapy of the present invention can be used to restore “normal”vasculature response in a patient who has undergone a radicalprostatectomy procedure where normal circulatory control may not returnfor 6-8 months post operatively.

The therapy of the present invention therefore has application in femaledysfunction and urogenital aging conditions such as vaginal lubrication,vaginal engorgement, pain during intercourse (dyspareunia), urogenitalinfections; and urogenitalia as affected by post-menopause, diabetes,vascular disease, estrogen depletion conditions, sexual dysfunction, andidiosyncratic vaginal dryness, respectively. In such situations, thetherapy of the present invention works to improve blood flow to thevagina leading to vaginal engorgement promoting better circulation(lubrication).

It is understood that any agent which provides a dose range of NO isintended to be included within the scope of the present invention. Thus,in accordance with the invention, an agent may be NO, an NO-likesubstance, a substance which directly releases NO (e.g., an NO donor) orcauses the release of NO, a substance having NO-like activity or effect,a substance which directly activates guanyl cyclase, or a substance thatprolongs the actions of the 2nd messenger molecule cGMP, such as a PDEinhibitor. Regardless of which of such agent or agents is employed inthe methods of the invention, what is important is that an enhancedlevel of NO is achieved, or the effect of an enhanced level of NO isachieved. The enhanced level is delivered to the vasculature such thatnormal vascular tone is achieved by a mechanism which involvesnormalizing levels of ET, thereby restoring the tone of the targetmicrovasculature.

It should also be understood that the methods of the invention includethe administration of an agent or agents as described above, (i.e, NO,an NO-like substance, a substance which directly releases NO (e.g., anNO donor) or causes the release of NO, a substance having NO-likeactivity or effect, or a substance which directly activates guanylcyclase), either acutely or chronically. Acute administration isadministration of a finite duration and can be, for example, as short asthat associated with treatment of ED, wherein administration takes placefor a prescribed period of time (e.g., up to several hours) at discreteinstances when the affect of the administration (penile erection) isdesired. Acute administration can also be of longer, finite duration.Chronic administration is administration of a continuous and indefiniteduration, and can be, for example, administration associated with achronic condition such as that involving inappropriate vasoconstrictionof the renal vasculature, where chronic administration is necessary torestore normal renal function.

The methods of the present invention are also applicable to treatingvascular conditions wherein there is no appreciable decrease orinhibition of endogenous NO. Such vascular conditions occur, forexample, when endothelial cells experience high shear from rapidmovement of red blood cells passing in contact with, or in closeproximity to, endothelial cells, resulting in increased ET. The methodsof the invention restore NO/ET balance. High shear is associated with,for example, drug therapy and atherosclerosis.

While the invention has been particularly shown and described withreference to certain embodiments, it will be understood by those skilledin the art that various other changes in form and detail may be madewithout departing from the spirit and scope of the invention.

All scientific papers and patents referred to in this specification areincorporated in totality by reference herein.

Quantitative Study

The study detailed herein quantitatively characterizes the level ofexogenous NO required to restore ‘normal’ vascular function followingthe acute and chronic blockade of NO synthase. Referring to the Figures,and in particular FIG. 1, the concentration-response relationship withincreasing levels of sodium nitroprusside (SNP) is markedly shifted forboth acute and chronic NO synthase blockade treated rats. Theconcentration-mean arterial pressure response curves were divided intotwo groups, concentrations that did not and those that did induce alowering of mean arterial pressure in the controls. A similar increasedsensitivity to low levels of SNP in the L-NAME treated rats wasdemonstrated both in acute and chronic phases of NO synthase blockadetreatment. This level of SNP administration (0.5 to 8 ug/kg per minute)did not significantly decrease mean arterial pressure in control ratsbut did result in a marked decrease in mean arterial pressure.

Referring now to FIG. 2 there may be seen an illustrative example ofthis finding: the depressor response to 2 ug/kg per minute in the NOsynthase blockade phase was superimposed over the 2 ug/kg per minuteresponse in the control period. The mean arterial pressure loweringinduced by 12-32 ug/kg per minute induced a similar lowering in bothcontrol and treated rats (see FIG. 1, lower panel), indicating aconvergence with respect to the depressor response to SNP.

Referring now to FIG. 3 it may be seen that the cumulative glyceryltrinitrate concentration-mean arterial pressure response demonstratedresults similar to SNP. The cumulative concentration-mean arterialpressure response curve was also shifted leftward in the NO synthaseblockade treated rats. Again, the similar trend of concentrations thatdo not lower mean arterial pressure in the controls, almost completelyreversed the NO synthase blockade induced hypertension.

Further studies assessed the impact of different vasoactive systems onthe relationship between nitric oxide and endothelin and, morespecifically, the low dose effects of nitric oxide and the suppressionof local levels of endothelin (ET), which cause vasodilation and anormalization of vascular tone in focal regions of the circulation thatare, at least in part, NO deficient. In these studies, L-NAME wasadministered to increase blood pressure, and two other vasodilatoragents were employed: isopropylnorepinephrine (INE, a B₁/B₂ agonist, seeFIG. 8) and the α₁ blocker prazosin (see FIG. 9). INE activates a cAMPmediated signal transduction system, and prazosin decreases the activityof an IP₃ signal transduction system.

FIGS. 8 and 9 provide more detailed information on the mechanismunderlying the increased sensitivity of mean arterial pressure to NOfollowing NO synthase blockade. As can be seen from FIGS. 8 and 9,neither of these two vasodilator agents was able to normalize theexcessive vasoconstriction that follows NO blockade.

Specifically, the two curves on the left-hand side of FIG. 8 clearlydemonstrate that the dose response of mean arterial pressure to INE isidentical both before and after nitric oxide synthase blockade,indicating that the signal mediated by another vasodilator, INE, isunchanged in the presence or absence of nitric oxide. It is widely knownthat the mechanism of action of INE is via the activation of cAMPmediated signal transduction. In contrast the curves on the right-handside of FIG. 8 indicate that there is an increase in sensitivity of meanarterial pressure to the NO donor SNP following the blockade of NOsynthase.

From a mechanistic standpoint, INE causes vasodilation by the activationof the cAMP signal transduction system in the vasculature, whereas SNPcauses vasodilation by the activation of the cGMP signal transductionsystem or by direct effects of NO (or an equivalent). The absence of ashift in sensitivity of mean arterial pressure to INE after NO blockadeindicates that the increased sensitivity to NO donors such as SNP isindependent of the cAMP signal transduction system, and may be directlydependent on the cGMP signal transduction system.

FIG. 9 illustrates that increased sensitivity to nitric oxide donorsoccurs following NO blockade, but does not occur following treatmentwith an α₁ receptor antagonist (prazosin). As prazosin is a secondvasodilator agent, similar to INE, these agents thus present twoexamples of different vasodilator mechanisms that do not influence therelationship between nitric oxide and endothelin, which relationship isin accordance with the methods of the present invention.

Therefore, to summarize the data presented in FIGS. 8 and 9, these datapresent examples demonstrating the relationship between nitric oxide andendothelin and the effects of a low-dose NO therapy on normalizing theaffected circulation with respect to endothelin and maintaining and/orrestoring vascular tone. These data also demonstrate that the imbalancein vascular tone that follows NO synthase blockade is not due toangiotensin II (data not shown), the sympathetic nervous system, orvasopressin (for example, via the IP₃ system), but is specific to thecGMP signal transduction system or direct effects of nitric oxide or itsequivalent. The data further indicate that the addition of an α₁receptor antagonist, in contrast to an endothelin receptor antagonist,does not restore a normal level of vascular sensitivity. This is inaccordance with the invention in that decreased levels of NO (viaL-NAME) result in a marked up-regulation of endothelin, such as may beexplained by an uncoupling of cGMP signalling.

FIG. 10 is similar in principle to FIG. 2 and provides a furtherquantitation of the ‘microdose’ level of exogenous NO that maintains anormal level of vascular tone following nitric oxide synthase blockadewith L-NAME. The graph of FIG. 10 illustrates that administering a levelof SNP that lowers blood pressure by 8 mmHg completely prevents thedevelopment of hypertension following even maximal NO synthase blockade(which is usually 40 mmHg). Thus, in accordance with the invention, itcan be seen that a microdose of SNP causes only a minimum level ofvasodilation, but completely prevents the excessive vasoconstrictionwhich occurs following high level NO synthase blockade using L-NAME.

Further evidence supports that nitric oxide chronically suppresses theeffects of endothelin. As shown in FIG. 11, even normal levels of NOinduce changes in the vasculature by countering the actions ofendothelin. In FIG. 11 (top panel), there can be seen an increase in thesensitivity of mean arterial pressure to SNP following NO synthaseblockade, and a decrease in the sensitivity to SNP in the presence ofPD145065, an endothelin receptor antagonist. The rightward shift in thecurve for PD145065 (under control conditions) clearly indicates that theresponse to NO by itself has been severely blunted. The bottom panel ofFIG. 11 similarly indicates that the increased sensitivity to the NOdonor GTN in response to treatment with L-NAME is abolished in thepresence of PD145065. These results indicate that endothelin receptorsare required to maintain the normal level of nitric oxide vasodilatorycapacity under control conditions.

As would be apparent to a person of ordinary skill in the art, it isreasonable to use the rat as a model for the affected vascular systemsdiscussed herein, such as, for example the pudendal and penisvasculature, and to extend such studies to appropriate dosages andtherapies for other subjects, such as humans. As is evidenced byMordenti, “Man versus Beast Pharmacokinetic Scaling in Mammals”, J.Pharm. Sci. 75:1028-1040 (1986) and similar articles, dosage forms foranimals, such as for example rats, can be and are widely used directlyto establish dosage levels in human applications. One of the presentinventors contributed to the development of a bioassay of erectilefunction in a rat model at least as early as 1991 (Heaton et al., J.Urol. 145:1099-1102, 1991), and also helped demonstrate in comparativetests of erectile function in humans and rats, that the narrow effectivedose window of an orally administered drug, apomorphine, is almostidentical when suitably adjusted for the differences in body weight astaught by Mordenti, cited above (Heaton et al., Urology 45:200-206,1995).

Effect of NO in Renal Vasculature

In essence, the kidney functions as a reverse filter in that almost allof the contents of the blood are filtered into beginning “urine” of thekidney and the kidney specifically reabsorbs what it wants to retainlater (in the nephrons and loop of Henle). A physical force, called therenal interstitial hydrostatic pressure (RIHP), in the tissues of thekidney can have a profound effect on this process. Increased RIHPpresents a physical force opposing the reabsorption process affectingreabsorption of sodium, water and other parts of the beginning filteredurine. If not reabsorbed the result is a diuretic response(natriuresis). In cases of low RIHP the opposite occurs. Removal of thephysical force opposing reabsorption results in volume accumulation(more blood volume=higher blood pressure). This pressure-mediatednatriuresis is explained by the fact that some of the blood vessels inthe kidney are not “auto regulated” (much like the penile vasculature),such that the pressure generated in the kidney tissue (RIHP) is dictatedby the level of vasoconstriction/kidney perfusion. Excessivevasoconstriction results in a decrease in RIHP, thereby removing astrong mechanism by which the kidney prevents the reabsorption of thecontents of filtered urine.

It is possible to simulate a type of renal failure, where excessivevasoconstriction predominates. In these circumstances a volumeconservation situation is created. This simulation is carried out bytreatment of anaesthetized rats which are fitted with instrumentationfor measuring RIHP and mean arterial blood pressure with NO synthaseblockers (L-NAME), The results from such experiments are depicted inFIGS. 5, 6, and 7 which illustrate “raw” pressure tracings of an exampleof these preparations (Methods written below, see EXPERIMENTAL ASPECTSOF STUDIES REPORTED: Effects of NO in Renal Vasculature). The tracesillustrate that administration of NO synthase blocker L-NAME, results ina sharp decline in RIHP (FIG. 5) consequent upon vasoconstriction of thevasculature. Administration of the NO precursor L-Arginine (150-200mg/kg per min) reversed the renal vasoconstriction (as measured by RIHPchanges—see FIG. 6) but did not alter the level of mean arterialpressure. When the L-Arginine administration is stopped (with continuedadministration of L-NAME, the RIHP once again sharply declines asillustrated in FIG. 7.

Clinical Data: For erectile dysfunction reversal with microdoses of NOGeneral Methods. Measurements were made in a clinical erectiledysfunction (ED) laboratory in patients with previously diagnosed ED.These patients were being evaluated for the purpose of optimization oftheir intracernous injection dosing. All men were assessed using theQueen's University Human Sexuality Group Protocol (Kingston, Ontario,Canada).

Case 1

The first patient was a man with total erectile dysfunction of 18months. History of hypertension, myocardial infarct (×2), coronaryartery by-pass graft surgery, cerebral vascular accident and peripheralvascular disease. He was prescribed 0.2 mg/hr nitro patch (GTN,Ciba-Geigy) with no effect on systemic blood pressure. The therapy with0.2 mg/hr nitro patch was on 2 occasions with 100% successfulintercourse. He had angina on the second try. This result supports theview that the quantity of NO administered was working at a levelsignificantly lower than quantities typically used.

Case 2

This patient was a man with no response to intra cavernosal injectiontherapy with conventional drugs. 0.2 mg/hr nitro patch (Ciba-Geigy)followed by 10 mcg PGE1. The patient experienced the first erection in 4years (predating radical prostate surgery).

The concentration of glyceryl trinitrate (the typical form of NO donorderived from Nitrospray or Nitropatches) has been reported in theliterature for such delivery routes to be in the order of 200 to 400pg/ml of plasma (Sun et al., J. Clin. Pharmacol. 35:390, 1995). Based onthe clinical case studies performed, it was noted that the beneficialeffects of a 0.2 mg/h patch are observed after 20 to 30 minutes. Thiscorresponds to a plasma concentration of 100 pg/ml. In respect of theapplication of the invention to ED therapy a preferred range of NO agent(such as GTN) is a steady state plasma concentration of about 50 toabout 200 pg/ml. This range corresponds to the “window” referred toabove as illustrated in FIG. 4.

Support for the proposal that the mechanism of action of the NO donorsdelivered at microdoses disclosed herein, are not directly vasodilatory,can be accomplished by giving animals NOS blocker high doses to createhypertension. This would be followed by infusion of an endothelinantagonist at a concentration which would almost completely reverse thehypertension induced by the NOS blocker. Subsequently, an NO donor, orcombination of NO donors is infused. The concentration response curvefrom this infusion should now be similar to that obtained in controlanimals. In other words, the doses of NO which will cause a lowering ofpressure will be at higher values, namely 10 to 24 times higher that inan L-NAME blocked animal alone thereby showing that high doses of NO arevasodilatory and lower ones are, on their own, not vasodilatory. Rather,they act to suppress ET.

While the routes of administration of the NO donors reported hereinclude intracavernous (IC) injection of NO donor, or by nasal spray orby patch, the present invention includes administration by means oftopical creams, pharmaceutically acceptable organic and inorganiccarrier substances suitable for parenteral, enteral, intraurethral,vaginal application, or transmucosal application via, for example, therespiratory tract (e.g., by inhalation, such as through intranasalapplication), which do not deleteriously react with the activecompounds.

Compositions of the invention are administered to subjects in abiologically compatible form suitable for pharmaceutical administrationin vivo. By “biologically compatible form suitable for administration invivo” is meant a form of the active compounds of the invention to beadministered in which any toxic effects are outweighed by thetherapeutic effects of the active compounds of the invention. The termsubject is intended to include living organisms in which a response canbe elicited, e.g., mammals. Examples of subjects include humans, dogs,cats, mice, rats, and transgenic species thereof.

Administration of a therapeutically active amount of the therapeuticcompositions of the present invention is defined as an amount effective,at dosages and for periods of time necessary to achieve the desiredresult. For example, a therapeutically active amount of active compoundsof the invention may vary according to factors such as the diseasestate, age, sex, and weight of the individual, and the ability of anagent or combination of agents of the invention to elicit a desiredresponse in the individual. Dosage regimens may be adjusted to providethe optimum therapeutic response. For example, several divided doses maybe administered or the dose may be proportionally reduced as indicatedby the exigencies of the therapeutic situation.

The active compounds (e.g., SNP) may be administered in a convenientmanner such as by injection (subcutaneous, intravenous, intracavernous,etc.), oral administration, inhalation, transdermal application, rectaladministration, urethral administration, vaginal administration, orintracavernous introduction. Depending on the route of administration,the active compound or compounds may be coated in a material to protectthe compound(s) from the action of enzymes, acids and other naturalconditions which may inactivate the compound(s), or facilitate or enabledelivery of said compound(s).

A SNP composition (or other NO donor) or as a separate agent can beadministered to a subject in an appropriate carrier or diluent,co-administered with enzyme inhibitors or in an appropriate carrier suchas liposomes. The term “pharmaceutically acceptable carrier” as usedherein is intended to include diluents such as saline and aqueous buffersolutions and vehicles of solid, liquid or gas phase. To administer anagent or agents of the present invention by other than parenteraladministration, it may be necessary to coat the active compound(s) ofthe invention with, or co-administer the agent or agents of the presentinvention with, a material to prevent its inactivation. Liposomesinclude water-in-oil-in-water emulsions as well as conventionalliposomes (Strejan et al., J. Neuroimmunol 7:27 1984). The activecompound(s) may also be administered parenterally or intraperitoneally.Dispersions can also be prepared in glycerol, liquid polyethyleneglycols, and mixtures thereof in oils and other solutions. Underordinary conditions of storage and use, these preparations may contain apreservative to prevent the growth of microorganisms, stabilityenhancers and compounds to preserve physical characteristics that areneeded for appropriate delivery.

Pharmaceutical compositions suitable for injectable use include sterileaqueous solutions (where water soluble) or dispersions and sterilepowders for the extemporaneous preparation of sterile injectablesolutions or dispersion. In all cases, the composition must be sterileand must be fluid to the extent that easy syringability exits. It mustbe stable under the conditions of manufacture and storage and must bepreserved against the contaminating action of microorganisms such asbacteria and fungi. The pharmaceutically acceptable carrier can be asolvent or dispersion medium containing, for example, water, ethanol,polyol (for example, glycerol, propylene glycol, and liquid polyethyleneglycol, and the like), and suitable mixtures thereof. The properfluidity can be maintained, for example, by the use of a coating such aslecithin, by the maintenance of the required particle size in the caseof dispersion and by the use of surfactants. Prevention of the action ofmicroorganisms can be achieved by various antibacterial and antifungalagents, for example, parabens, chlorobutanol, phenol, ascorbic acid,thimerosal, and the like. In many cases, it will be preferable toinclude isotonic agents, for example, sugars, polyalcohols such asmannitol, and sorbitol, or sodium chloride in the composition. Prolongedabsorption of the injectable compositions can be brought about byincluding in the composition an agent which delays absorption, forexample, aluminum monostearate and gelatin.

Sterile injectable solutions can be prepared by incorporating activecompound (e.g., SNP) or compounds in the required amount in anappropriate solvent with one or a combination of ingredients enumeratedabove, as required, followed by filter sterilization. Generally,dispersions are prepared by incorporating the active compound into asterile vehicle which contains a basic dispersion medium and therequired other ingredients from those enumerated above. In the case ofsterile powders for the preparation of sterile injectable solutions, thepreferred methods of preparation are vacuum drying and freeze-dryingwhich yields a powder of an active ingredient of the invention plus anyadditional desired ingredient from a previously sterile-filteredsolution thereof.

When an active compound(s) is suitably protected, as described above,the composition may be orally administered, for example, with an inertdiluent or an assimilable edible carrier. As used herein“pharmaceutically acceptable carrier” includes any and all solvents,dispersion media, coatings, antibacterial and antifungal agents,isotonic and absorption delaying agents, and the like. The use of suchmedica and agents for pharmaceutically active substances is well knownin the art. Except insofar as any conventional media or agent isincompatible with the active compound, use thereof in the therapeuticcompositions is contemplated. Supplementary active compounds can also beincorporated into the compositions.

It is especially advantageous to formulate parenteral compositions indosage unit form for ease of administration and uniformity of dosage.Dosage unit form as used herein refers to physically discrete unitssuited as unitary dosages for mammalian subjects to be treated; eachunit containing a predetermined quantity of active compound calculatedto produce the desired therapeutic effect in association with therequired pharmaceutical carrier. The specification for the dosage unitforms of the invention are dictated by and directly dependent on (a) theunique characteristics of the active compound and the particulartherapeutic effect to be achieved, and (b) the limitations inherent inthe art of compounding such an active compound for the therapeutictreatment of individuals.

Experimental Aspects of Studies Reported

Quantitative Study

Animals

Male Sprague-Dawley rats (325 to 400 g) obtained from Charles RiverLaboratories (Montreal, Canada) were housed individually underconditions of 12-hour light/dark cycle, with room temperature at 22 to24° C., and were provided with Purina rodent chow and tap water adlibitum for at least 2 days before any experiments were started.

Measurement of MAP and Short Acting Drug Administration

The surgical method was based on the technique of Thompson et al.(Hypertens. 20:809, 1992). In brief, rats were anaesthetized withketamine/xylazine (70/5 mg/kg i.p.), and the descending aorta distal tothe kidneys was catheterized with small bore Teflon tubing (0.012 ini.d., 30 gauge, Cole-Parmer, Laval, Quebec, Canada) inserted into vinyltubing (0.02 in i.d., 0.060 in, 23 gauge). The inferior vena cava wasalso catheterized distal to the kidneys with small bore Teflon tubing(0.012 in i.d., 30 gauge, Cole-Parmer). The catheters were filled withheparinized saline (10 IU/ml) and held in place by a small amount ofcyanoacrylate glue at the puncture site. The catheters were tunnelledsubcutaneously and exteriorized at the back of the neck and sutured inplace. Two days after surgery, MAP could be recorded (MacLab DAS,ADInstruments, Milford, Mass.). After connection, an equilibrationperiod of approximately 30 minutes allowed for the determination of thesteady state level of MAP before any recording began. Baseline MAP wasdetermined from readings averaged over 5 minutes, taken from each rat at15 minute intervals for at least 1 hour prior to the start of anyexperiment.

Sodium Nitroprusside and Glyceryl Trinitrate Concentration—Mean ArterialPressure Response Curves Following Acute and ChronicN^(ω)-nitro-L-arginine Methyl Ester

Rats were randomly assigned treatment with N^(ω)-nitro-L-arginine methylester (L-NAME) for 30 minutes (100 mg/kg, intraperitoneally) or 12 days(100 mg/kg, in drinking water) or tap water. Two days prior to the dayof the experiment rats were instrumented with catheters, as describedabove. Following baseline measurements of MAP, rats were given ainfusions of sodium nitroprusside (SNP, 0.5 to 32 ug/kg per minutedissolved in 0.9% sterile saline) with a step-wise increase inconcentration every two minutes. Rats were allowed 30 minutes to recoverfrom the SNP administration. Rats were then given infusions of glyceryltrinitrate (GTN, 0.5 to 32 ug/kg per minute dissolved in 0.9% sterilesaline) with a step-wise increase in concentration every two minutes.

Throughout all of these pharmacological manipulations, MAP and HR wererecorded at a sampling rate of 100 Hz and the data was stored on a diskdrive for later analysis.

Effects of NO in Renal Vasculature

Surgical preparation: Experiments were performed in male Sprague-Dawleyrates, 250 to 330 g, obtained from Charles River Laboratories (Montreal,Canada). Food (Purina rat chow) and water were provided ad libitumthroughout the study. Rats were acclimatized for at least a week priorto experimentation in group housing under conditions of a 12-hourlight/dark cycle, with room temperature at 22 to 24° C. 3 to 4 daysprior to each experimental day, rats were instrumented with an aorticcatheter as described in detail previously (Thompson et al.,Hypertens.20:809, 1992). In brief, the rates were anaesthetized withketamine hydrochloride (70 mg/kg i.p. (Rogarsetic, Rogar/STB Inc.,Montreal, PQ) and xylazine hydrochloride (5 mg/kg i.p. (Rompum, HaverInc., Etobickoe, ON) and placed on a heating pad to maintain a constantbody temperature of 37° C. Additional ketamine was given, as necessary,during surgery. Following an abdominal incision, the descending aortadistal to the kidneys was catheterized with smallbore Teflon tubing(i.d.=0.012 in, o.d.=0.030 in, 30 gauge, Cole-Parmer, Laval, Quebec,Canada), inserted into vinyl tubing (i.d.=0.02 in, o.d.=0.060 in, 23gauge). The catheter was filled with heparinized saline (50 IU/ml, Grade1-A Heparin Sodium salt, Sigma Chemical Co., St Louis) and held in placeby a small amount of cyanoacrylate tissue glue (Lepage Ltd., Brampton,ON). The catheter was then flushed with a small volume (0.1-0.3 ml) ofheparinized saline (50 IU/ml) and left entirely inside the abdominalcavity until the day of the RIHP measurements. The abdominal incisionwas sutured with 6-0 silk braided thread (Ethicon Ltd., Peterborough,Ontario). The rats were allowed to recover for 2 to 5 days, during whichthey were housed individually under the same conditions as describedabove. Rats were re-weighed following the recovery period and rats thathad lost >30 g were considered to have not sufficiently recovered fromthe surgery and hence, were excluded from the study (Haskins, S. C.,Postoperative care, In: Methods of Animal Experimentation, Vol. III PartA, eds. Gay et al. (Academic Press Inc., Orlando, 1986)).

Experimental Procedure: The RIHP measurements were carried out in ratsanaesthetized with thiobutabarbital sodium (Inactin, 100 mg/kg i.p.,Byk-Gulden, Constance, Germany). This anaesthetic is used mostfrequently by others for the study of RIHP and PN and, in preliminarystudies, yielded similar results to those studies compared to aKetamine/Xylazine anaesthetic preparation.

Rats were placed on a heating pad to maintain a constant bodytemperature of 37° C. and the abdominal incision was reopened.Hematocrits were determined by the microcapillary tube method fromarterial blood samples (300 μl) obtained from the arterial catheter.Only rates in which the hematocrit was found to be between 40 and 45percent were subsequently used. Rates with hematocrits out of this rangewere considered to be hemodynamically challenged due to the blood lossduring surgery and, since reductions in hematocrit can compromisecardiovascular function, were not used in this study (Haskins, S. C.,Postoperative care, In: Methods of Animal Experimentation, Vol. III PartA , eds. Gay et al. (Academic Press Inc., Orlando, 1986); Pirkle et al.,Endocrin. 110:7, 1982; Houttuin et al., Am J. Physiol. 223:63, 1972).

The arterial catheter, inserted previously, was attached to a pressuretransducer (model CDX3, Cobe), and the pulsatile signal recorded using aphysiograph (Beckman, model R511 or MacLab, ADInstruments Pty Ltd.,Castle Hill, Australia). Small sections of the aorta (<0.5 cm proximalto the right kidney), mesenteric and celiac arteries were isolated andsilk ligatures were placed loosely around the vessels.

RIHP was measured by implanting a cannula into the lateral side of theleft renal cortex (Garcia-Estañ et al., Am. J. Physiol., 256:F63, 1989).The RIHP catheter was constructed by inserting a small core of porouspolyethylene matrix material (2 mm, 35 μm pore size, Bel-Art Products,Pequannoc, N.J.) into the heat expanded end of a polyethylene catheter(PE-50, i.d.=0.023 in, o.d.=0.038 in×10-20 cm) such that approximatelyone-third of the matrix extends beyond the tubing. This techniqueensures that tissue does not block the catheter while allowing formeasurement of hydrostatic pressure (Roman et al., Am. J. Physiol.248:F190, 1985; Ott et al., J. Appl. Physiol. 38:937, 1975). A 3 mm deephole was made in the lateral surface of the left kidney with anelectrocautery needle (26 gauge) and current was passed through theneedle for approximately 3 to 5 seconds. Bleeding was completely stoppedby applying soft pressure with a cotton swab. The kidney was kept drybefore implanting the RIHP catheter. The RIHP catheter was inserted intothe hole and then sealed to the surface of the kidney capsule withcyanoacrylate. The RIHP catheter was similarly attached to thephysiograph via the pressure transducer. Lack of pulsatile pressureensured that the catheter was not in a blood vessel. To further checkthe location of the catheter two procedures were performed: (i) a smallvolume (100-200 μl) of saline (10 IU/ml heparin) was slowly infused inorder to obtain a characteristic increase in RIHP (Ott et al., 1975) and(ii) a RIHP response to renal vein occlusion (RVO) was observed(Garcia-Estañ et al., Am. J. Physiol., 256:F63, 1989). Rats that failedto show these characteristic responses (FIG. 2-1) were excluded from theexperiment

After a 10 to 15 minute equilibration period, the RVO response from theRIHP catheter and a pulsatile recording from the arterial catheter werere-confirmed and a baseline MAP and RIHP were recorded. During thecontrol periods of the experiment, the exposed abdominal cavity was keptmoist by covering with a wet gauze patch and 0.9% saline. In eachexperiment, arterial pressure was manipulated systematically from low tohigh MAP by sequentially tightening the ligatures around the upperaorta, celiac artery and mesenteric artery. Pressure changes wereinitially maintained for approximately 5 to 7 minutes in order to ensurethat both MAP and RIHP equilibrate to the new steady state. As it wasdetermined that RIHP equilibrated in less than 3 minutes all date wascollected within this time. The RVO-RIHP response was checkedperiodically after reaching different arterial pressures. This sequenceof arterial pressure manipulations was repeated after a 10 to 15 minutecontrol period at baseline MAP and RIHP. The position of the RIHPcatheter was verified at the end of each experiment and was typicallyfound in the corticomedullary junction.

Those skilled in the art will recognize, or be able to ascertain throughroutine experimentation, equivalents to the specific embodimentsdescribed herein. Such equivalents are considered to be within the scopeof the invention and are covered by the appended claims.

We claim:
 1. A method for treating a urogenital disorder in a femalesubject, said method comprising: administering to said female subject anagent that enhances NO while maintaining normal systemic vascular tone,to treat said urogenital disorder in said female subject.
 2. The methodfor treating a urogenital disorder of claim 1, wherein said urogenitaldisorder is selected from the group consisting of decreased vaginallubrication, decreased vaginal engorgement, pain during intercourse,dyspareunia, urogenital infections, effects on urogenitalia due topost-menopause or diabetes, vascular disease, estrogen depletionconditions, sexual dysfunction, and idiosyncratic vaginal dryness. 3.The method for treating a urogenital disorder of claim 2, wherein saidurogenital disorder is selected from the group consisting of decreasedvaginal engorgement, pain during intercourse and dyspareunia.
 4. Themethod for treating a urogenital disorder of claim 3, wherein saidurogenital disorder is dyspareunia.
 5. The method for treating aurogenital disorder of claim 1, wherein said administration of saidagent is selected from the group consisting of oral, sublingual, buccal,intravenous, transdermal, vaginal, rectal, by inhalation, enteral, andparental.
 6. The method for treating a urogenital disorder of claim 1,wherein administration of said agent is at concentration that is about ½to about {fraction (1/20)} of a concentration of said agent required toinduce vasodilation in a healthy vasculature.
 7. The method for treatinga urogenital disorder of claim 6, wherein administration of said agentis at concentration that is about ¼ to about {fraction (1/20)} of aconcentration of said agent required to induce vasodilation in healthyvasculature.
 8. The method for treating a urogenital disorder of claim7, wherein administration of said agent is at concentration that isabout ⅛ to about {fraction (1/16)} of a concentration of said agentrequired to induce vasodilation in healthy vasculature.
 9. The methodfor treating a urogenital disorder of claim 1, wherein said agent whichenhances NO is GTN, and said level of administration is a plasmaconcentration below about 250 pg/ml of GTN.
 10. The method for treatinga urogenital disorder of claim 1, wherein said agent is selected fromthe group consisting of NO, CO. NO donors, CO donors, activators ofguanylyl cyclase, PDE inhibitors, and substances which produce an effectequivalent to that of NO.
 11. The method for treating a urogenitaldisorder of claim 10, wherein said agent is a PDE inhibitor.
 12. Themethod for treating a urogenital disorder of claim 10, wherein said NOdonor is selected from the group consisting of glyceryl trinitrate,isosorbide 5-mononitrate, isosorbide dinitrate, pentaerythritoltetranitrate, erythrityl tetranitrate, sodium nitroprusside,3-morpholinosydnonimine molsidomine, S-nitroso-N-acetylpenicillamine,S-nitrosoglutathione, and N-hydroxy-L-arginine.
 13. The method fortreating a urogenital disorder of claim 12, wherein said NO donor isglyceryl trinitrate (GTN).
 14. A method for improving blood flow to thevagina, said method comprising: administering to a female subject anagent that enhances NO while maintaining normal systemic vascular tone,to improve blood flow to the vagina.
 15. A method for treatingdyspareunia in a female subject, said method comprising: administeringto said female subject an agent that enhances NO while maintainingnormal systemic vascular tone, to treat dyspareunia in said femalesubject.
 16. A method for treating a urogenital disorder in a femalesubject, said method comprising: topically administering to said femalesubject an agent that enhances NO while maintaining normal systemicvascular tone, to treat said urogenital disorder in said female subject.17. A method for restoring NO/ET balance in a female subject, saidmethod comprising: administering to said female subject an agent thatenhances NO while maintaining normal systemic vascular tone, to restoreNO/ET balance in said female subject.
 18. A method for treating anestrogen depletion condition in a female subject, said methodcomprising: administering to said female subject an agent that enhancesNO while maintaining normal systemic vascular tone, to treat saidestrogen depletion condition in said female subject.
 19. A method forimproving vaginal blood flow in a female subject, said methodcomprising: administering to said female subject an agent that enhancesNO while maintaining normal systemic vascular tone, to improve vaginalblood flow in said female subject.
 20. A method for improving vaginallubrication in a female subject, said method comprising: administeringto said female subject an agent that enhances NO while maintainingnormal systemic vascular tone, to improve vaginal lubrication in saidfemale subject.